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’Invisible’ Objects Closer

Photonics.comMay 2007
LIVERPOOL, England, May 3, 2007 -- A unique computer model designed by a mathematician at the University of Liverpool has shown it is possible to make objects, such as airplanes and submarines, appear invisible at close range.

Scientists predict invisibility will be possible for objects of any shape and size within the next decade. They have already created an "invisibility cloak" made out of "metamaterial," which can bend electromagnetic radiation -- such as visible light, radar or microwaves -- around a spherical space, making an object within this region appear invisible. (See also: Theoretical Blueprint for Invisibility Cloak Reported)

But until now, they could only make objects appear invisible from far away. Liverpool mathematician Sébastien Guenneau, with Frédéric Zolla and professor André Nicolet from the University of Marseille, have proven -- using a computer model called GETDP (for General Environment for the Treatment of Discrete Problems) -- that objects can also be made to appear invisible from close range when light travels in waves rather than beams.

They said metamaterials could be of use in military technology, such as in the construction of fighter jets and submarines, but that it will be some years before invisibility cloaks can be developed for human beings.

Guenneau said, "The shape and structure of airplanes make them ideal objects for cloaking, as they have a fixed structure and movement pattern. Human beings and animals are more difficult, as their movement is very flexible, so the cloak -- as it is designed at the moment -- would easily be seen when the person or animal made any sudden movement. "

He said a cloak -- such as the one worn by the Harry Potter character, for example -- is not yet possible "but it is a good example of what we are trying to move toward. Using this new computer model, we can prove that light can bend around an object under a cloak and is not diffracted by the object."

This happens because the metamaterial that makes up the cloak stretches the metrics of space, similar to what heavy planets and stars do for the metrics of space-time in Einstein's general relativity theory, Guenneau said. In order for the cloaking device to work in the first place, light has to separate into two or more waves resulting in a new wave pattern. "Within this pattern, we get light and dark regions which are needed in order for an object to appear invisible," he said.

Until now, it was not clear if photons -- particles that make up all forms of light -- can split and form new waves when the light source is close to the object.

"If we use ray optic techniques, where light travels in beams, photons break down at close range and the object does not appear invisible. If we study light as it travels in waves, however, invisibility is maintained," Guenneau said.

A material engineered from artificial matter not found in nature. The artificial makeup and design of metamaterials give them intrinsic properties not common to conventional materials that are exploited as light waves and sound waves interact with them. One of the most active areas of research involving metamaterials currently explores materials with a negative refractive index. In optics, these negative refractive index materials show promise in the fabrication of lenses that can achieve...

The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...